- August 01, 2008
Sleeves became a standard on flexographic presses for package printing years ago due to their numerous advantages. The integration of sleeve technology in narrow web flexo presses has been a topic of discussion for many years. However, only individual label printers have used the sleeve option as yet. In the meantime, there are an increasing number of signs that the trend toward sleeves could become established in the narrow web printing sector too. At Labelexpo Europe 2007, Gallus, Nilpeter, Omet, MPS, and Gidue demonstrated printing presses with sleeve technology.
Advantages of Sleeves
The main advantages of sleeves include:
• faster installation and dismantling, which allows a significant reduction of setup times;
• lower costs compared to impression cylinders of steel or aluminum;
• abolition of gears or bearing rings, thus doing away with wearing parts;
• lighter weight (1–10 kg instead of 30–40 kg) that makes handling much easier for operators, etc.
This list is by no means exhaustive and could be continued. In view of their considerable advantages, sleeve technology will conquer the narrow web market sooner or later.
Fast Job Change
The fast job change regularly demonstrated by Gallus would not be possible without the use of printing form sleeves. Label manufacturers such as the Swiss firm Pago AG have been using sleeves for many years. Nevertheless, many label printers still are very skeptical when it comes to using this technology. However, Torsten Scholz, product manager at Gallus Druckmaschinen GmbH, is convinced there will be a significant increase in the use of sleeves in the narrow web sector over the coming months.
The company sent out invitations to an event under the motto "Sleeves to the power of 3" in spring 2008. Company owner Bernard Pauwels reported on the experience gained in the past by the Belgian printers Conti-Label Pauwels NV in Eeklo with the Gallus EM 410 S. He attributed the double-digit increase in productivity largely to the reduction in setup times that could be achieved using the sleeve technology.
At the same event Carl Ostermann Erben GmbH (COE) pointed out that a trend could be observed toward seamless and endless photopolymer sleeves. This technology really comes into its own for large print runs, numerous changes in forms, or frequent repeat orders.
Since the printing forms artwork is already in a circular form, these sleeves also are predestined for orders with critical color registers. Typical fields of use are thus flexible packaging, serviettes and tissue products, shrink sleeves, and increasingly all types of labels.
These are also the main fields of application named by Torsten Scholz. In his opinion their use is profitable in particular for label printers that have to meet high quality standards in UV flexo printing.
The second promising target group are companies that process film substrates, e.g., for flexible packaging, shrink sleeves, etc., in narrow web printing.
Individual Calculation of Whether a Sleeve Is Worthwhile
Gallus and COE agree that individual calculations as to whether the use of a sleeve is worthwhile are needed for a number of these orders. In the initial phase, it is often difficult to correctly estimate all of the parameters for profitability.
Unlike wide web flexo printing, an important factor for narrow web printing is the availability of a printing process that allows a high quality with low printing form costs: offset printing. But sleeve technology is being used more and more in this method too, above all as an alternative to the complex printing cartridges.
Predestined for Film Printing and Larger Machine Widths
Bert van den Brink, CEO of MPS, also can confirm the growing interest in sleeve technology. However, he is unable to say precisely whether this interest reflects the actual needs of the market or whether it has been generated by the wealth of information on the topic of sleeves.
It is a fact, however, that between 25% and 30% of MPS’s customers now decide on a sleeve machine. This relatively high share is probably influenced by the fact that many users of MPS machines are active in market segments that are ideal for the use of sleeves, e.g., processing film products in a high print quality.
The sleeve share continues to rise with the machine's printing width. Since sleeves have significant weight advantages over impression cylinders, they also greatly facilitate the handling of wider machines.
The range of machines offered by the Italian manufacturer Gidue thus includes the Athena series, available in web widths of 530 mm, 630 mm, and 730 mm, and which is designed for sleeve technology. Other machine manufacturers do not restrict the sleeve design to certain models or web widths. The EM-S and RCS series in particular from Gallus are suitable for use with sleeves. At Nilpeter this is primarily the FA line.
MPS can, in principle, use printing form sleeves on all machine models. However, the procedure whereby blocks are mounted on a sleeve and then fitted onto an air cylinder outside the machine so that it can be inserted into the printing unit like a conventional impression cylinder is only practical for endless motifs.
The setup advantages of sleeves only come into their own if sleeves can be changed directly in the machine on air axes that are installed as a standard feature. In the case of MPS, this is only possible with EF H model that has been designed as a hybrid machine.
Standards Are High in Narrow Web Printing
The fact that printing form sleeves have not been able to establish themselves in narrow web printing up to now may be related to a fact that has as yet been somewhat overlooked in public discussions. The majority of sleeves are matched to the requirements of wide web flexo printing. But completely different criteria are important in narrow web printing.
For example, higher demands are made on concentricity or dimensional stability in this market segment. This has various reasons. Thus, the standards for picture motif are higher than in wide web flexo. The images are generally smaller, calling for a higher print quality. What's more, narrow web printers use almost exclusively a No. 60 fine screen.
“At first glance, the narrow web widths implied that there would be hardly any problems with aspects such as register accuracy in sleeves for label printing,” says rotec CEO Mario Busshoff. But compared to packaging flexo printing on central cylinder machines, higher screen definitions are used as standards in label printing, meaning higher demands on the printing form.
Special Features of Narrow Web Printing
Users in the label sector are used to using the entire web width wherever possible when using impression cylinders. This is why the printing forms have to display a high dimensional stability right up to the edge zone.
The demands on concentricity and above all diameter accuracy have a maximum plus-minus tolerance of only one hundredth of a millimeter. It is much more difficult for plastic sleeves to fulfill these requirements than the impression cylinders of metal. And in the case of compressible sleeves, which can be used to positively influence the printing characteristics during flexo printing, these high accuracies have to be achieved despite the porous material structure.
Temperature changes that may occur, for example, through the production process in the printing press, should not affect the concentricity. The frequently used combination of several printing methods in one printing press is another reason why a high dimensional stability is very important in narrow web printing. Dimensional fluctuations in the flexo print sleeve would inevitably lead to register problems for the other printing methods.
Special Label Version Developed
Due to the requirements described above, a new sleeve has been developed especially for use in the label segment. The new product goes by the name of Blue Light Label and has a very high dimensional stability right through to the outer edge zones of the sleeve.
The printing characteristics and service life have been further improved compared to the standard version. The newly developed multilayer structure of synthetic resins and composite fibers guarantees constant characteristics even after intensive use. These include above all the greater dimensional stability, constant parallelism of the sleeve during printing, and the exact register behavior.
This is based on high-precision grinding that allows a TIR value (Total Indicator Reading, i.e., maximum deviation of the outer diameter during a 360 deg rotation) of below 0.025 mm – measured on a carrier cylinder with a TIR value of less than or equal to 0.005 mm.
The new sleeves are available from a wall thickness of 12 mm and up to a maximum face width of 600 mm. The sturdy yet at the same time lightweight sleeves are designed for conventional plate mounting with foamed adhesive tape. They are suitable for all plate and adhesive tape strengths and have an extremely resistant surface of polyurethane with a density of 75 Shore D. The surface is resistant to scratches and cuts as well as solvents and allows a simple removal of the adhesive tape.
During Labelexpo 2007, sleeves from this series were demonstrated on machines from Nilpeter, MPS, and Mark Andy. MPS also confirms that a noticeable improvement in quality can be achieved with the new type of sleeve.
Bert van den Brink compares the development of the sleeve to the history of UV flexo printing in the narrow web sector. The radiation-hardened printing inks also had to pass through a long phase of changing successes before they reached today's level.
He also believes that the adoption of the sleeve technology from the wide web sector has not yet been completed and still needs a little time. After all, there are numerous significant differences to the narrow web segment, e.g., as regard to printing inks, substrates, machine design, etc. In order to push the development faster in future, users are needed who will actively cooperate in the development.
The newly developed sleeve is very interesting for label printers since it combines the features listed above with a high dimensional stability and good concentricity. This opens up not only advantages in terms of setup times or ergonomics (professional organizations demand a reduction in the weight of parts that have to be handled when operating printing presses) for users but also qualitative advantages. But the majority of advantages are offered by rotary printing forms themselves, e.g., Cyrel round sleeves.
Modern Machines Combined with Sleeve Technology
If printers are planning to use sleeves in the narrow web sector, they do so with suitable machines wherever possible. Although users still can profit from the use of sleeves with retrofit or conventional machines, the optimization potential with such a constellation is relatively low. This is why Mario Busshoff warns users to “keep their fingers off sleeves if the machine is not in principle designed for this technology.” Machine manufacturers also believe that retrofitting is complicated and, in the majority of cases, is not really worthwhile.
The more up-to-date the installed machine, the easier it is to use sleeve technology, says Torsten Scholz from Gallus. And new sleeve technologies could offer far more possibilities for reducing setup times, increasing production speeds and print quality, and saving costs wherever press-ready blocks are stuck to sleeves at present. Examples of such technologies are plate-on-sleeve forms or endless seamless variants, as well as directly laser-engraved sleeves such as are currently propagated by firms such as Hell Gravure Systems.
Gallus is currently carrying out internal tests with laser-engraved flexo printing forms. Photopolymer endless sleeves on the other hand, such as those offered by the Cyrel-round technology, are already in successful use.
The machine manufacturers unanimously agree that users should look into the last-named sleeve technologies in particular if they are searching for a high print quality in flexo printing in the long term. Live demonstrations with Cyrel-round sleeves were presented during this year's Labelexpo on the stands of Mark Andy and MPS. A special challenge in terms of print quality is the printing of special colors in a scale set, for example. This assumes an extremely high register accuracy to prevent fluctuations or deviations in the color. It is hard to achieve the necessary precision with manually mounted printing plates.
Disadvantages or Advantages?
The costs of the investment and space requirements for their storage are often quoted as disadvantages of sleeves. Michael Jagiella, technical manager at the firm of Gundlach Logo in Mahlberg, is of a different opinion.
His company produces with a total of five narrow web machines. Sleeves are used on three printing presses. The costs savings during procurement are among the most important reasons for using Blue-Light sleeves.
With normal equipment, an impression cylinder with matching gear and format disc would be needed for every print length. With a sleeve, however, all that is needed is a carrier cylinder onto which the matching sleeve and format ring can be fitted depending on the format.
What's more, plastic sleeves also are easier to store, according to Michael Jagiella. And printing forms that have been pre-assembled outside the printing press offer great advantages, especially when processing orders with several changes of types, such as are common at Gundlach Logo. He sees even more possibilities with the Cyrel-round technology, which the printers are currently testing for certain orders.
rotec huelsensysteme | www.rotec-sleeves.com
Gallus | www.gallus.org
Nilpeter | www.nilpeter.com
Omet | www.matik.com
MPS | www.mps-america.com
Gidue | www.gidue.com
Carl Ostermann Erben GmbH | www.coe-bremen.de/
Mark Andy | www.markandy.com
DuPont Cyrel | www.cyrel.com
Hell Gravure Systems | www.hell-gravure-systems.com